Experts from the Centers for Disease Control say that approximately 13 percent of inmates at two California prisons where a fungal infection has killed three dozen prisoners have developed immunity from prior exposure and do not need to be moved to other facilities, the Associated Press reports.

Last fall, a federal judge ordered the state to move about 2,600 inmates in the Avenal and Pleasant Valley state prisons to other facilities. Certain groups of inmates—Filipinos, blacks and those suffering from diabetes and HIV—are believed to be more susceptible to the illness. So-called valley fever is caused by a soil-borne fungus natural to soils in dry areas.

The CDC experts suggest fine-tuning that broad net by not moving prisoners who exhibit immunity to the fungus.

The CDC earlier this year reported that, besides the illness and death toll among prisoners, three prison employees had died from valley fever and 103 others became ill between January 2009 and June 2013, the AP reported in February.

The federal-court appointed receiver controlling prison medical care is reviewing the more recent report concerning immunity screening, a spokeswoman said.